Single fiber layer structure of micron or nano fibers and multi-layer structure of micron and nano fibers applied in separator for battery

ABSTRACT

A single fiber layer structure of micron or nano fibers, and a multi-layer structure of micron and nano fibers are provided. The single fiber layer structure of micron fibers comprises a web of micron fibers and an impregnating resin, and has a pore size of 1 nm-500 nm. The web of micron fibers is formed by plural interweaved micron fibers (D≧1 μm). The single fiber layer structure of nano fibers comprises a web of nano fibers formed by plural interweaved nano fibers (D&lt;1 μm). The multi-layer structure of micron and nano fibers comprises a web of interweaved micron fibers, a web of nano fibers formed by plural nano fibers interweaved on the web of micron fibers, a mixture layer formed by parts of the interweaved nano and micron fibers, and a resin at least impregnating the mixture layer and parts of the micron fibers of the web of micron fibers.

This application claims the benefit of Taiwan application Serial No.101146967, filed Dec. 12, 2012, the disclosure of which is incorporatedby reference herein in its entirety.

TECHNICAL FIELD

The disclosure relates in general to a single fiber layer structure offiber, and more particularly to a single fiber layer structure of micronor nano fibers and a multi-layer structure of micron and nano fibersapplied in separator for battery.

BACKGROUND

If electric cars and portable electronic products adopt paper-thin powerbattery, the demand for paper-thin and high-efficient separator willincrease dramatically. According to the forecast of market size anddemand for global vehicle power battery, the demand will increase to0.562 billion square meters (m²) and the price will increase to 2.2USD/m² by the end of 2013. Along with the rapid growth in the market ofelectric cars, the development of separator will depend on the marketdemand of vehicles and production scale.

Most separators for power battery currently available in the market aremainly porous film types. A thin-type single-layer or multi-layer filmis formed by way of melt stretching, coating and drying, or hotpressing. Let the separator applied in lithium battery and provided bythe Celgard, LLC of USA and the Ube Industries Ltd. of Japan be takenfor example. Porous separator having a thickness less than 20 um isformed by melt stretching process. The flux of high polymer whenextruded is crystallized under a tensile stress and forms a lamellaestructure which is perpendicular to extrusion direction and is arrangedin parallel. Then, the lamellar structure is processed with heattreatment to obtain a hard elastic material. Then, slit pores are formedwhen lamellae is separated after the polymer film is stretched. Then,the polymer film is processed with thermal setting treatment to form amicroporous film. However, the above method for manufacturing amicroporous film has following disadvantages. The pore size and theporosity are hard to control, and the horizontal strength of themicroporous film is poor because the polymer film is stretched only in avertical manner. Japanese companies, such as Asahi Kasei, Tonen, andMitsui Chemicals, form a porous separator having a thickness less than20um by using thermally induced phase separation method. Details ofthermally induced phase separation method are as follows. The polymer isdissolved in a solvent having high boiling point and low volatility athigher temperature to form a homogeneous solution. Next, as thetemperature cools down, the solution generates liquid-solid phaseseparation or liquid-liquid phase separation. Then, the high boilingpoint solvent is extracted by a volatile reagent, and is further driedto obtain a high polymer micro-porous film having a specific shape andstructure. Although it is easier to control the pore size, the pore sizedistribution and the porosity in the thermally induced phase separationmethod than in the method used by the Celgard, the thermally inducedphase separation method requires a large volume of solvent during themanufacturing process and employs relatively complicated procedures.

The Teijin Ltd. and the Japan Vilene Co. Ltd. of Japan use a compositematerial and a pore forming material to form a porous separator (PETnon-woven fabric) having a thickness less than 30 μm and an average poresize greater than 5 μm. The pore size is controlled by the pore formingmaterial. The Mitsubishi Corporation of Japan uses fibers of differentdiameters to form a separator (PET non-woven fabric) having a thicknessless than 30 μm and an average pore size>10 μm. The pore size iscontrolled by composite conditions. The Degussa AG of Germany forms asupporting material (PET non-woven fabric) by using single fiber webspinning technology in which the supporting material is coated withinorganic powder to form a separator having a thickness less than 20 μm.However, the single fiber web spinning technology has followingdisadvantages. The pore size and the porosity are hard to control, andthe horizontal strength of the porous separator is poor because theporous separator is stretched only in a vertical manner. In addition,the pore size is controlled by the amount of inorganic powder and thebinder to be greater than 5 μm. Although each of the above methods formanufacturing porous separator by way of stretching or adding aninorganic powder has its own advantages and disadvantages, these methodshave the same problem of the pore size being too large (greater than 5μm), and the porous separator, when the porous separator is applied inseparator for power battery, cannot effectively separate the positivepolarity and the negative polarity of the battery and will deterioratethe performance of the power battery.

Therefore, how to provide a separator for power battery which matchesthe needs of development and low cost and at the same time produceexcellent separation effect has become a prominent task for theindustries.

SUMMARY

The disclosure is directed to a single fiber layer structure of micronor nano fibers and a multi-layer structure of micron and nano fibersapplied in a battery separator.

According to one embodiment, a multi-layer structure of micron and nanofibers applied in a battery is provided. The multi-layer structure ofmicron and nano fibers comprises a web of micron fibers, a web of nanofibers, a mixture layer of fibers, and a resin. The web of micron fibersis formed by a plurality of interweaved micron fibers whose diameter isgreater than or equal to 1 μm. The web of nano fibers is formed by aplurality of nano fibers interweaved on the web of micron fibers,wherein the plurality of nano fibers has a diameter less than 1 μm. Themixture layer of fibers is located between the web of nano fibers andthe web of micron fibers, and comprises parts of the plurality ofinterweaved nano and micron fibers. The resin at least impregnates themixture layer of fibers and parts of the micron fibers of the web ofmicron fibers. In an experimental example, the multi-layer structure ofmicron and nano fibers has a porosity of 45%-80%.

According to another embodiment, a single fiber layer structure ofmicron fibers applied in battery is provided. The single fiber layerstructure of micron fibers comprises a web of micron fibers and a resin.The web of micron fibers is formed by a plurality of micron fibers whosediameter is greater than or equal to 1 μm. The micron fibers createpores after being impregnated with resin. The structure of micron fibershas a pore size of 1 nm-500 nm. In an experimental example, thestructure of micron fibers has an average pore size of 100 nm-350 nm. Inanother experimental example, the structure of micron fibers has anaverage pore size of 100 nm-300 nm.

According to an alternative embodiment, a single fiber layer structureof nano fibers applied in a battery is provided. The single fiber layerstructure of nano fibers comprises a web of nano fibers formed by aplurality of interweaved nano fibers whose diameter is less than 1 μm.The structure of nano fibers has a pore size of 1 nm-500 nm. In anexperimental example, the structure of nano fibers has a pore size of 10nm-500 nm and an average pore size of 100-350 nm.

The above and other aspects of the disclosure will become betterunderstood with regard to the following detailed description of thenon-limiting embodiment (s). The following description is made withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a comparison based on results of full battery test withvoltage 3.65V between a Celgard-2320 and a single-layer of micron ornano fibers and a multi-layer structure of micron and nano fibers ofembodiments of the present invention (experimental examples 2, 5, 11);

FIG. 2 is a comparison based on results of 500 cycles ofcharge/discharge test with charge/discharge rate 3 C between aCelgard-2320 and a single-layer of micron or nano fibers and amulti-layer structure of micron and nano fibers of embodiments of thepresent invention (experimental examples 2, 5, 11);

FIG. 3 is a comparison based on self discharge test at temperature of60° C. between a Celgard-2320 and a single-layer of micron or nanofibers and a multi-layer structure of micron and nano fibers ofembodiments of the present invention;

FIG. 4A is a cross-sectional view of a Celgard-2320 shot with a scanningelectron microscope (SEM);

FIG. 4B is a cross-sectional view of a multi-layer structure of micronand nano fibers of an embodiment shot with an SEM.

In the following detailed description, for purposes of explanation, aplurality of specific details are set forth in order to provide athorough understanding of the disclosed embodiments. It will beapparent, however, that one or more embodiments may be practiced withoutthese specific details. In other instances, well-known structures anddevices are schematically shown in order to simplify the drawing.

DETAILED DESCRIPTION

A structure of fibers applied in a separator for a battery such as powerlithium battery is disclosed in an embodiment of the invention. Thestructure of fibers comprises a single fiber layer structure of micronfibers, a single fiber layer structure of nano fibers, and a multi-layerstructure of micron and nano fibers. The technology for processing thedisclosed structures of fibers is not complicated, and the pore size,the pore size distribution and the porosity of the structures of fibersare easy to control. The manufactured structures of fibers have smallpore size, and produce excellent separation effect of separating thepositive polarity and negative polarity when applied in a separator forpower battery.

<Structure of Micron Fibers>

A single fiber layer structure of micron fibers applied in a battery isprovided according to an embodiment. The single fiber layer structure ofmicron fibers comprises a web of micron fibers and a resin. The web ofmicron fibers is formed by a plurality of micron fibers whose diameteris greater than or equal to 1 μm. Then, the web of micron fibers iscoated with a mixture solution containing the resin, and is furtherwater bathed to remove a solvent of the mixture solution to obtain theweb of micron fibers. In an embodiment, the web of micron fibers can beprocessed with densification treatment (by using a calender machine) tochange the thickness of the web of micron fibers, either before thecoating process or after the water bathing process, so as to obtain athin-type separator of micron fibers having a pore size of 1 nm-500 nm.

In an embodiment, the thin-type separator of micron fibers has a poresize of 1 nm-450 nm and an average pore size of 100 nm-350 nm. In anembodiment, the web of micron fibers (that is, separator thickness) hasa thickness of 10 μm-40 μm.

In an embodiment, the thin-type separator of micron fibers has a poresize of 100 nm-400 nm and an average pore size of 250 nm-350 nm. In anembodiment, the web of micron fibers has a final thickness of 25 μm(that is, separator thickness).

In another embodiment, the plurality of micron fibers has a diameter of1 μm-10 μm. Then, the web of micron fibers is processed withdensification treatment to form a thin-type separator of micron fibershaving a pore size of 200 nm-500 nm and an average pore size of 250nm-350 nm.

In an embodiment, the micron fibers are formed by materials such aspolyethylene terephthalate (PET), polyethylene (PE), or polypropylene(PP).

In an embodiment, the resin is such as polyvinylidene fluoride (PVDF)dissolved in N-Methyl-2-pyrrolidon (NMP), or polyacrylonitrile (PAN)dissolved in dimethylacetamide (DMAc), or other materials satisfying theconditions of application. In an embodiment, the weight ratio betweenthe micron fibers and the resin is 10:5.

<Single Fiber Layer Structure of Nano Fiber>

In the present embodiment, a single fiber layer structure of nano fibersapplied in a battery is provided. The single fiber layer structure ofnano fibers comprises a web of nano fibers formed by a plurality ofinterweaved nano fibers whose diameter is less than 1 μm byelectro-spinning a polymer solution. Following electro-spinningtreatment, the web of nano fibers is processed with densificationtreatment (by using a calender machine) to form a thin-type separator ofnano fibers having a pore size of 1 nm-500 nm.

In an embodiment, the thin-type separator of nano fibers has a pore sizeof 1 nm-500 nm and an average pore size of 100 nm-350 nm. In anembodiment, the web of nano fibers has a final thickness of 5 μm-40 μm(that is, separator thickness).

In an embodiment, the thin-type separator of nano fibers has an averagepore size of 50 nm-200 nm and a porosity of 65%.

In an embodiment, the thin-type separator of nano fibers has a pore sizeof 250 nm-550 nm and an average pore size of 300 nm-450 nm. In anembodiment, the web of nano fibers has a final thickness of 20 μm (thatis, separator thickness).

In another embodiment, the plurality of electro-spun nano fibers has adiameter of 1 nm-500 nm, and an average diameter of 10 nm-300 nm. Inanother embodiment, the plurality of electro-spun nano fibers has adiameter of 10 nm-500 nm and an average diameter of 100 nm-300 nm.Before the electro-spun nano fibers are processed with densificationtreatment, the electro-spun nano fibers have a pore size of 500 nm-900nm and an average pore size of 700 nm -800 nm. Then, the electro-spunnano fibers are processed with densification treatment to form athin-type separator of nano fibers having a pore size of 100 nm-500 nmand an average pore size of 200 nm-350 nm.

In an embodiment, the nano fibers are formed by materials such as pitchfiber, PAN fiber, phenolic fiber, or an ion polymer whose repeat unit isformed according to structural formulas [I] and [II]:

wherein, R1 comprises phenyl sulfonate, and R2 is formed by materialsselected from following group comprising:

R3 represents amine or sulfonate, X repesents chloride, bromide oriodide, m and n are numbers of repeat units, and m/n is between1/99-99/1.

In an embodiment, the weight ratio between benzene sulfonic acid, amineand sulfonate is 80:10:10 and 50:25:25.

<Multi-Layer Structure of Micron and Nano Fibers>

In the present embodiment, a multi-layer structure of micron and nanofibers applied in a battery is provided. The multi-layer structure ofmicron and nano fibers comprises a web of nano fibers, a web of micronfibers, a mixture layer of fibers and a resin. The web of micron fibersis formed by a plurality of interweaved micron fibers whose diameter isgreater than or equal to 1 μm. The web of nano fibers is formed by aplurality of nano fibers interweaved on the web of micron fibers. Theplurality of nano fibers has a diameter less than 1 μm. The mixturelayer of fibers is formed by parts of the interweaved nano and micronfibers and located between the webs of nano and micron fibers. The resinat least impregnates the mixture layer of fibers and parts of the micronfibers of the web of micron fibers. The lastly manufactured multi-layerstructure of micron and nano fibers (micron+nano) has a pore size of0.001 μm-0.7 μm and a porosity greater than or equal to 45%. In anembodiment, most micron and nano fibers have a pore size of 100 nm-400nm.

In an embodiment, the lastly manufactured multi-layer structure ofmicron and nano fibers has a pore size of 1 nm-400 nm, an average poresize of 50 nm-200 nm, and a porosity of 45%-80%.

In an embodiment, the lastly manufactured multi-layer structure ofmicron and nano fibers has a pore size of 00 nm-500 nm, an average poresize of 300 nm-400 nm, a porosity greater than or equal to 45%, and theratio between micron and nano fibers is 10:1. In an embodiment, themicron fibers have a pore size of 10 nm-700 nm and a diameter of 1 μm-10μm. In an embodiment, the nano fibers have a pore size of 10 nm-500 nm,and a diameter of 1 nm-700 nm. In an embodiment, the nano fibers have anaverage diameter of 500 nm.

The manufacturing process of the multi-layer structure of micron andnano fibers is disclosed below. Electro-spinning treatment is applied ona polymer solution to interweave the plurality of nano fibers on the webof micron fibers to form a web of micron fibers and a web of nanofibers. In an embodiment, the weight ratio between the micron fibers andthe nano fibers of the obtained composite structure is 10:10, and thelastly manufactured multi-layer structure of micron and nano fibers hasa pore size of 10 nm-300 nm and an average pore size of 50 nm-150 nm. Inanother embodiment, the weight ratio between the micron fibers and thenano fibers of the obtained composite structure is 10:5, and the lastlymanufactured multi-layer structure of micron and nano fibers has a poresize of 50 nm-400 nm and an average pore size of 100 nm-200 nm.

The resin of the multi-layer structure of micron and nano fibers atleast impregnates the mixture layer of fibers and parts of the micronfibers of the web of micron fibers. After the web of nano fibers isformed by the plurality of nano fibers interweaved on the web of micronfibers by electro-spinning a polymer solution, one side of the web ofmicron fibers is coated with a mixture solution containing the resin andis further water bathed to remove a solvent of the mixture solution toreduce the mixture layer of fibers and pore size of the parts of themicron fibers of the web of micron fibers.

In an embodiment, the weight ratio between the micron fibers, the nanofibers and the resin is 60:20:20 and 65:20:15. The resin is such as PVDFdissolved in NMP, PAN dissolved in DMAc, or other materials satisfyingthe conditions of application.

In an embodiment, the web of interweaved nano and micron fibers can beprocessed with densification treatment (by using a calender machine)before the coating process is applied. In addition, having beenprocessed with water bathing process, the multi-layer structure ofmicron and nano fibers can be processed with densification treatment toform a thin-type composite separator of fibers. In an embodiment, theweb of densified micron fibers has a thickness of 10-25 μm and anaverage thickness of 1 μm-5 μm, and the multi-layer structure ofdensified micron and nano fibers has a thickness less than 30 μm. Themicron fibers and the nano fibers can be formed by materials asdisclosed above, or other materials satisfying the conditions ofapplication.

In an embodiment, the nano fibers are electro-spun on a surface ofmicron non-woven fabric to form a porous supporting material which isfurther thinned by a rolling machine. Then, the surface of micronnon-woven fabric is coated with resin; alternatively, the poroussupporting material is impregnated with resin and is rolled such thatresin is interposed into the gap of supporting material through micronmesh layer to reduce the pores to form a thin-type two-layer porousstructure of micron and nano fibers having a thickness less than 30 μm.The two-layer porous structure of micron and nano fibers can be directlyapplied in a separator for power battery, such as thin-type lithiumbattery product or high power lithium battery product. The multi-layerstructure of micron and nano fibers of the present embodiment has a poresize of 0.001 μm-0.7 μm. Most pore sizes of the two-layer structure ofmicron and nano fibers are between 0.1 μm-0.4 μm and are relativelysmaller than that of conventional non-woven fabric being greater than 5μm. When the two-layer structure of micron and nano fibers is applied ina separator for power battery, the separation effect of separating thepositive and the negative polarities of the battery can be largelyenhanced. In addition, the multi-layer structure of micron and nanofibers of the present embodiment has a porosity of 45-80%, and mostporosities are above 50%. In comparison to existing porous separatorshaving a porosity of 40%, the two-layer structure of micron and nanofibers of the present embodiment has higher porosity (higher ionconduction velocity). Therefore, when the separator using themulti-layer structure of micron and nano fibers of the presentembodiment is applied in a power battery product, the separator producesbetter separation effect due to smaller pore size and higher porosity.

The contents of parts of experimental example of single fiber layerstructure of micron or nano fiber and multi-layer structure of micronand nano fibers are disclosed below. The contents comprise manufacturingmethods and tests of properties of fiber structure. However, anyone whois skilled in the technology field of the present invention willunderstand that experimental contents of experimental examples, such asmanufacturing procedures and selected materials, are for exemplificationonly, not for limiting the scope of protection of the present invention,and various modifications and variations can be made to themanufacturing procedures or selection of materials according to theneeds in actual implementation.

<Single Fiber Layer Structure of Micron Fibers-Experimental Examples1-4>

Benzene Sulfonic Acid Amine Sulfonate Experimental Example 1 80 wt % 10wt % 10 wt % Experimental Example 2 65 wt % 20 wt % 15 wt % ExperimentalExample 3 50 wt % 25 wt % 25 wt % Experimental Example 4 30 wt % 35 wt %35 wt %

Experimental Example 1

polypropylene (PP) is electro-spun to form a non-woven fabric having abasic weight of 10 g/m² and a thickness of 70 μm. Next, the non-wovenfabric is processed with densification treatment by using a calendermachine (at a rotation speed of 15 Hz and a temperature of 70° C.) toform a thin-type non-woven fabric having a thickness of 20 μm. Then,polyvinylidene fluoride (PVDF with molecular weight being 50/mol) andalumina (2%, particle size is 13 nm) are dissolved inN-Methyl-2-pyrrolidon (NMP) solution to form a mixture solution. Then, asurface of the polypropylene (PP) non-woven fabric base is coated withthe mixture solution (PVDF:NMP=15:85) at a rotation speed of 34 rpm andis further water bathed to remove NMP solvent. Then, the separator (at arotation speed of 15 Hz and a temperature of 70° C.) is processed withdensification treatment to by using a calender machine to form athin-type separator of micron fibers (fiber: PVDF=10:5). The propertiesof the thin-type separator of micron fibers are measured as below. Thethin-type separator of micron fibers has a thickness of 25 μm, a poresize of 100 nm-400 nm, an average pore size of 250 nm-350 nm, a porosityof 47%, and a McMullin value of 6. The McMullin value is a ratio betweenseparator resistance and electrolyte resistance, and the smaller theMcMullin value, the higher the ionic conductivity.

Experimental Example 2

polypropylene (PP) is electro-spun to form a non-woven fabric having abasic weight of 10 g/m², and a thickness of 70 μm. Next, the non-wovenfabric is processed with the thinning treatment by using a calendermachine (at a rotation speed of 15 Hz and a temperature of 70° C.) toform a thin-type non-woven fabric having a thickness of 20 μm. Then,polyvinylidene fluoride (PVDF with molecular weight being 20 g/mol) isdissolved in N-Methyl-2-pyrrolidon (NMP) solution to form a mixturesolution (PVDF:NMP=7:93). Then, a surface of the thin-type non-wovenfabric is coated with the mixture solution to reduce size of poresbetween fibers and is further water bathed to remove NMP solvent. Then,the separator is processed with densification treatment by using acalender machine (at a rotation speed of 15 Hz and a temperature of 70°C.) to form a thin-type separator of micron fibers (fiber:PVDF=10:5).The properties of the thin-type separator of micron fibers are measuredas below. The thin-type separator of micron fibers has a thickness of 26μm, a pore size of 10 nm-500 nm, an average pore size of 100 nm-300 nm,a porosity of 50%, and a McMullin value of 8.

Experimental Example 3

polypropylene (PP) is electro-spun to form a non-woven fabric having abasic weight of 10 g/m² and a thickness of 70 μm. Next, the non-wovenfabric is processed with thinning treatment by using a calender machine(at a rotation speed of 15 Hz and a temperature of 70° C.) to form athin-type non-woven fabric having a thickness of 20 μm. Then,polyacrylonitrile (PAN-procured from the Tong-Hwa Synthetic FiberCompany Limited) is dissolved in dimethylacetamide (DMAc)(PAN:DMAc=13:87). Then, a surface of the thin-type non-woven fabric iscoated with the mixture solution to reduce size of pores between fibersand is further water bathed to remove DMAc solvent. Then, the separatoris processed with densification treatment by using a calender machine(at a rotation speed of 15 Hz and a temperature of 70° C.) to form athin-type separator of micron fibers (fiber:PVDF=10:5). The propertiesof the thin-type separator of micron fibers are measured as below. Thethin-type separator of micron fibers has a thickness of 23 μm, a poresize of 200 nm-450 nm, an average pore size of 250 nm-350 nm, a porosityof 45%, and a McMullin value of 9.

Experimental Example 4

polypropylene (PP) is electro-spun to form a non-woven fabric having abasic weight of 10 g/m². Next, the non-woven fabric is processed withdensification treatment by using a calender machine (at a rotation speedof 15 Hz and a temperature of 70° C.) to form a thin-type non-wovenfabric having a thickness of 20 μm. Then, polyvinylidene fluoride (PVDFwith molecular weight being 50 g/mol) and alumina (10%, particle size is13 nm) are dissolved in N-Methyl-2-pyrrolidon (NMP) solution to form amixture solution. Then, a surface of the polypropylene (PP) non-wovenfabric base is coated with the mixture solution (PVDF:NMP=15:85) at arotation speed of 34 rpm and is further water bathed to remove NMPsolvent. Then, the separator is processed with densification treatmentby using a calender machine (at a rotation speed of 15 Hz and atemperature of 70° C.) to form a thin-type separator of micron fibers(fiber:PVDF=10:5). The properties of the thin-type separator of micronfibers are measured as below. The thin-type separator of micron fibershas a thickness of 22 μm, a pore size of 10 nm-400 nm, an average poresize of 50 nm-200 nm, a porosity of 65%, and a McMullin value of 5.

It can be known from three of the four disclosed experimental examples1-4 of single fiber layer structure of micron fibers that the singlefiber layer structure of micron fibers of the present embodiment has apore size (such as 100-350 nm) being smaller than that of conventionalseparator (>5 μm) and has a porosity (>45%) higher than that ofconventional separator (40%). Therefore, the power battery using thestructure of the present embodiment as a separator film has betterperformance.

<Single Fiber Layer Structure of Nano Fiber: Experimental Examples 5-7>

Benzene Sulfonic Acid Amine Sulfonate Experimental Example 5 80 wt % 10wt % 10 wt % Experimental Example 6 50 wt % 25 wt % 25 wt % ExperimentalExample 7 30 wt % 35 wt % 35 wt %

Experimental Example 5

the ion polymer formed according to disclosed structural formulas iselectro-spun to form meshed nano polymer fiber having a diameter of 10nm-700 nm and used for forming a web of nano fibers. Next, the non-wovenfabric is processed with densification treatment by using a calendermachine (temperature 70° C.) to form a thin-type separator of nanofibers. The properties of the thin-type separator of micron fibers aremeasured as below. The thin-type separator of nano fibers has athickness of 20 μm, a pore size of 250 nm-550 nm, an average pore sizeof 300 nm-450 nm, a porosity of 65%, and a McMullin value of 6.

Experimental Example 6

the ion polymer formed according to disclosed structural formulas iselectro-spun to form meshed nano polymer fiber having a diameter of 100nm-500 nm and used for forming a web of nano fibers. Next, the non-wovenfabric is processed with densification treatment by using a calendermachine (temperature 70° C.) to form a thin-type separator of nanofibers. The properties of the thin-type separator of micron fibers aremeasured as below. The thin-type separator of nano fibers has athickness of 15 μm, a pore size of 10 nm-500 nm, an average pore size of100 nm-300 nm, a porosity of 55%, and a McMullin value of 7.

Experimental Example 7

the ion polymer formed according to disclosed structural formulas iselectro-spun to form meshed nano polymer fiber having a diameter of 10nm-300 nm and used for forming a web of nano fibers. Next, the non-wovenfabric is processed with densification treatment by using a calendermachine (temperature 70° C.) to form a thin-type separator of nanofibers. The properties of the thin-type separator of micron fibers aremeasured as below. The thin-type separator of nano fibers has athickness of 12 μm, a pore size of 1 nm-400 nm, an average pore size of50 nm-150 nm, a porosity of 75%, and a McMullin value of 5.

It can be known from two of the disclosed experimental examples 5-7 ofsingle fiber layer structure of nano fiber that the single fiber layerstructure of nano fiber of the present embodiment has a pore size (10nm-550 nm) less than that of conventional separator (>5 μm), and has aporosity (52%-75%) significantly higher than that of conventionalseparator (40%).

<Multi-Layer Structure of Micron and Nano Fibers: Experimental Examples8-11>

Benzene Sulfonic Acid Amine Sultanate Experimental Example 8 80 wt % 10wt % 10 wt % Experimental Example 9 65 wt % 20 wt % 15 wt % ExperimentalExample 10 50 wt % 25 wt % 25 wt % Experimental Example 11 30 wt % 35 wt% 35 wt %

Experimental Example 8

the ion polymer formed according to disclosed structural formulas havinga basic weight of 1 g/m² is electro-spun on one single side ofpolypropylene (PP) non-woven fabric having a basic weight of 10 g/m2 anda thickness of 70 μm to form a two-layer web of fiber. Then, thetwo-layer web of fibers is processed with thinning treatment by using acalender machine (at a rotation speed of 15 Hz and a temperature of 70°C.) to form a thinned PP non-woven fabric having a thickness of 20 μm.Then, polyvinylidene fluoride (PVDF with molecular weight being 20g/mol) dissolved in N-Methyl-2-pyrrolidon (NMP) solution to form amixture solution (PVDF:NMP=7:93). Then, a surface of the thinned PPnon-woven fabric is coated with the mixture solution to reduce size ofpores between fibers and is further water bathed to remove NMP solvent.Then, the separator is processed with densification treatment by using acalender machine (at a rotation speed of 15 Hz and a temperature of 70°C.) to form a thin-type composite separator of fibers (fiber:PVDF=11:5).The properties of the thin-type composite separator of fibers aremeasured as below. The thin-type separator of micron fibers has athickness of 22 μm, a pore size of 100 nm-400 nm, an average pore sizeof 150 nm-250 nm, a porosity of 53%, and a McMullin value of 6.

Experimental Example 9

the nano fiber of the ion polymer formed according to disclosedstructural formulas [I] having a basic weight of 10 g/m2 is electro-spunon one single side of polypropylene (PP) non-woven fabric having a basicweight of 10 g/m² and a thickness of 70 μm to form a two-layer web offiber. Then, the two-layer web of fibers is processed with thinningtreatment by using a calender machine (at a rotation speed of 15 Hz anda temperature of 70° C.) to form a thin-type composite separator offibers. The properties of the thin-type composite separator of fibersare measured as below. The thin-type separator of micron fibers has athickness of 30 μm, a pore size of 10 nm-300 nm, an average pore size of50 nm-150 nm, a porosity of 45%, and a McMullin value of 7.

Experimental Example 10

the nano fiber of the ion polymer having a basic weight of 5 g/m² iselectro-spun on one single side of polypropylene (PP) non-woven fabrichaving a basic weight of 10 g/m² and a thickness of 70 μm to form atwo-layer web of fiber. Next, the two-layer web of fibers is processedwith thinning treatment by using a calender machine (at a rotation speedof 15 Hz and a temperature of 70° C.) to form a thinned PP non-wovenfabric having a thickness of 23 μm. Then, polyacrylonitrile(PAN-procured from the Tong-Hwa Synthetic Fiber Company Limited) isdissolved in dimethylacetamide (DMAc) (PAN:DMAc=13:87). Then, a surfaceof the thin-type non-woven fabric is coated with the mixture solution toreduce size of pores between fibers and is further water bathed toremove DMAc solvent. Then, the separator is processed with densificationtreatment by using a calender machine (at a rotation speed of 15 Hz anda temperature of 70° C.) to form a thin-type composite separator offibers (fiber:PAN=15:5). The properties of the thin-type compositeseparator of fibers are measured as below. The thin-type separator ofmicron fibers has a thickness of 25 μm, a pore size of 50 nm-400 nm, anaverage pore size of 100 nm-200 nm, a porosity of 50%, and a McMullinvalue of 5.

Experimental Example 11

the nano fiber of the ion polymer having a basic weight of 5 g/m² iselectro-spun on one single side of polypropylene (PP) non-woven fabrichaving a basic weight of 10 g/m² and a thickness of 70 μm to form atwo-layer web of fiber. Next, the two-layer web of fibers is processedwith thinning treatment by using a calender machine (at a rotation speedof 15 Hz and a temperature of 70° C.) to form a thin-type non-wovenfabric having a thickness of 23 μm. Then, polyacrylonitrile(PAN-procured from the Tong-Hwa Synthetic Fiber Company Limited) isdissolved in dimethylacetamide (DMAc) (PAN:DMAc=8:92). Then, a surfaceof the thin-type non-woven fabric is coated with the mixture solution toreduce size of pores between fibers and is further water bathed toremove DMAc solvent. Then, the separator is processed with densificationtreatment by using a calender machine (at a rotation speed of 15 Hz anda temperature of 70° C.) to form a thin-type composite separator offibers (fiber:PAN=10:5). The properties of the thin-type compositeseparator of fibers are measured as below. The thin-type separator ofmicron fibers has a thickness of 20 μm, a pore size of 1 nm-300 nm, anaverage pore size of 50 nm-150 nm), a porosity of 70%, and a McMullinvalue of 5.

It can be known from three of the disclosed experimental examples 8-11of multi-layer structure of micron and nano fiber that the multi-layerstructure of micron and nano fibers of the present embodiment has a poresize (10 nm-400 nm) less than that of conventional separator (>5 μm) anda porosity (45-70%) significant higher than that of conventionalseparator (40%). Therefore, the power battery using the structure of thepresent embodiment as a separator film has better performance.

<Comparison Between Multi-Layer Structure of Micron and Nano Fibers ofEmbodiment of The Present Invention and Conventional Separators>

Table 1 shows a comparison of properties between single fiber layerstructure of micron or nano fiber and multi-layer structure of micronand nano fibers of experimental example and conventional separators ofthe Celgard, LLC and the Asahi Kasei.

Comparison of properties as illustrated in Table 1 shows that themulti-layer structure of micron and nano fibers of disclosed embodimentshas a very small pore size which can be as small as 0.15 μm, and hasbetter size stability, porosity and McMullin value, and the thermalshrinkage at temperature of 130° C. is 0. Therefore, battery separatorusing the multi-layer structure of micron and nano fibers of disclosedembodiments has better overall performance.

TABLE 1 Celgard, Asahi Experimental Experimental Experimental LLC KaseiExample 2 Example 5 Example 11 Base Tri-Layer Single- Micron Fibers NanoFibers Fiber Porous Layer Composite Film Porous Film Thickness 20 20 2620 20 (μm) Size <130° C. <130° C. >160° C. >160° C. >160° C. Stability(° C.) Thermal 42.5 84.5 0 0 0 Shrinkage (%, @ 130° C.) Porosity 40 4050 65 70 (%) Pore Size 0.1 0.1 0.2 0.35 0.15 (μm) Mechanical 13 20 19 1517 Strength (N/cm) McMullin 12 12 8 6 5<High Power Lithium Battery Discharge Capacitance and Self DischargeTest>

In following experiments, relevant tests are performed on a Celgard-2320(a separator of the Celgard, LLC) and a single fiber layer structure ofmicron or nano fibers and a multi-layer structure of micron and nanofibers of disclosed embodiments (such as experimental examples 2, 5,11).

1. Full Battery Test

Charge and discharge current (ampere) is normally represented by numberof times of battery marked capacity and is referred as capacity rate(C-rate), wherein C represents the volume of current during thecharge/discharge of battery. For example, when the marked capacity of acharge battery is 1.1 Ah, this indicates that the battery can last for 1hour if the discharge rate is 1.1 Ah (1 C) and can last for 5 hours ifthe discharge rate is 200 mA (0.2 C).

FIG. 1 is a comparison based on results of full battery test withvoltage 3.65V between a Celgard-2320 and a single-layer of micron ornano fibers and a multi-layer structure of micron and nano fibers ofembodiments of the present invention (experimental examples 2, 5, 11).In the present experiment, the battery is charged/discharged atdifferent discharge rates (C-rate), such as 1 C, 3 C, 5 C, 7 C, and 10C. The comparison of FIG. 1 shows that when the battery the battery ischarged/discharged at high discharge rates 5 C and 7 C, thecharge/discharge performances of the single fiber layer structure ofmicron fibers (experimental example 2), the single fiber layer structureof nano fiber (experimental example 5) and the multi-layer structure ofmicron and nano fibers (experimental example 11) of disclosedembodiments are all superior to that of the Celgard-2320. When dischargerate reaches 10 C, the charge/discharge performances of the single fiberlayer structure of nano fiber (experimental example 5) and themulti-layer structure of micron and nano fibers (experimental example11) are more significantly superior to that of the Celgard-2320.

2. Cyclic Charge/Discharge Test for Long Duration

FIG. 2 is a comparison based on results of 500 cycles ofcharge/discharge test with charge/discharge rate 3 C between aCelgard-2320 and a single-layer of micron or nano fibers and amulti-layer structure of micron and nano fibers of embodiments of thepresent invention (experimental examples 2, 5, 11). Under normal use,cycle life (number of cycles) of a lithium battery is more than 500cycles. The lithium battery can be charged/discharged for 1-500 cyclesfor a long duration at the charge/discharge rate 3 C/3 C. It can beknown from the results of FIG. 2 that after having beencharged/discharged for 500 cycles, all test samples havecharge/discharge efficiency of 100%.

3.Self Discharge Test: At Temperature of 60° C.

No matter a battery is used or not, as time passes by, the battery willexperience power loss due to various reasons. FIG. 3 is a comparisonbased on self discharge test at temperature of 60° C. between aCelgard-2320 and a single-layer of micron or nano fibers and amulti-layer structure of micron and nano fibers of embodiments of thepresent invention. It can be known from the results of FIG. 3 that after28 days, the ingle-layer structure of micron fibers and the Celgard-2320retain at least 91% of voltage, and the single fiber layer structure ofnano fibers retains 95% of voltage which is superior to that of theCelgard-2320 (91%).

4. Cross-Sectional View of Structure

FIG. 4A is a cross-sectional view of a Celgard-2320 shot with a scanningelectron microscope (SEM). FIG. 4B is a cross-sectional view of amulti-layer structure of micron and nano fibers of an embodiment shotwith an SEM. As indicated in FIG. 4A, the Celgard-2320 is a dry-typeporous film on which slit pores are formed when lamellae structure isseparated after the polymer film is vertically stretched, and isdifferent from the multi-layer structure of micron and nano fibers asillustrated in embodiment of FIG. 4B. The pore size and the porosity ofthe Celgard-2320 are hard to control, and the horizontal strength of theporous film is weaker. The structures of fibers of disclosed embodimentshave following advantages. The processing technology is not complicated,the pore size, the pore size distribution and the porosity are easy tocontrol, the manufactured structures of fibers have small pore size anduniform distribution of pore size, and excellent performance can beproduced when the structures of fibers of disclosed embodiments areapplied in separator for power battery.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed embodiments.It is intended that the specification and examples be considered asexemplary only, with a true scope of the disclosure being indicated bythe following claims and their equivalents.

What is claimed is:
 1. A multi-layer structure of micron and nano fibersapplied in a battery, comprising: a web of micron fibers formed by aplurality of interweaved micron fibers whose diameter is greater than orequal to 1 μm; a web of nano fibers formed by a plurality of nano fibersinterweaved on the web of micron fibers, wherein the plurality of nanofibers have a diameter less than 1 μm; a mixture layer of fibers locatedbetween the web of nano fibers and the web of micron fibers, wherein themixture layer of fibers comprises parts of the plurality of interweavednano and micron fibers; and a resin at least impregnating the mixturelayer of fibers and parts of the plurality of micron fibers of the webof micron fibers.
 2. The multi-layer structure of micron and nano fibersaccording to claim 1, having a pore size of 1 nm-700 nm and a porositygreater than or equal to 45%.
 3. The multi-layer structure of micron andnano fibers according to claim 1, having a porosity of 45%-80%.
 4. Themulti-layer structure of micron and nano fibers according to claim 1,wherein, the web of micron fibers has a pore size of 10 nm-700 nm, andthe web of nano fibers has a pore size of 10 nm-500 nm.
 5. Themulti-layer structure of micron and nano fibers according to claim 1,wherein a weight ratio between the plurality of micron fibers, theplurality of nano fibers and the resin is 60-65:20:20-15.
 6. Themulti-layer structure of micron and nano fibers according to claim 1,wherein the resin is polyvinylidene fluoride (PVDF) dissolved inN-Methyl-2-pyrrolidone (NMP) or polyacrylonitrile (PAN) dissolved indimethylacetamide (DMAc).
 7. The multi-layer structure of micron andnano fibers according to claim 1, wherein the web of nano fibers formedby the plurality of nano fibers interweaved on the web of micron fibersis formed by electro-spinning a polymer solution, one side of the web ofmicron fibers is coated with a mixture solution containing the resin andis further water bathed to remove a solvent of the mixture solution toreduce the mixture layer of fibers and pore size of parts of theplurality of micron fibers of the web of micron fibers.
 8. Themulti-layer structure of micron and nano fibers according to claim 1,wherein the plurality of micron fibers are formed by materials such aspolyethylene terephthalate (PET), polyethylene (PE), or polypropylene(PP) polymer, and the plurality of nano fibers are formed by materialssuch as pitch fiber, PAN fiber, phenolic fiber or an ion polymer whoserepeat unit is formed according to structural formulas [I] and [II]:

wherein, R₁ comprises benzene sulfonic acid, and R₂ is formed bymaterials selected from following group comprising:

R₃ represents amine or sulfonate, X represents chloride, bromide oriodide, m and n are numbers of repeat units, and m/n is between1/99-99/1.
 9. The multi-layer structure of micron and nano fibersaccording to claim 1, wherein when a weight ratio between micron andnano fibers is between 10:5 and 10:10, the multi-layer structure ofmicron and nano fibers has a pore size of 1 nm-400 nm and an averagepore size of 50 nm-200 nm.
 10. The multi-layer structure of micron andnano fibers according to claim 1, wherein the plurality of micron fibershave a diameter of 1 μm-10 μm, and the plurality of nano fibers have adiameter of 1 nm-700 nm.
 11. The multi-layer structure of micron andnano fibers according to claim 1, wherein the web of micron fibers has athicknesss of 10 μm-25 μm, the web of nano fibers has a thickness of 1μm-5 μm, and the multi-layer structure of micron and nano fibers has athickness less than 30 μm.